WO2021125563A1 - 항복비가 우수한 고강도 열연강판 및 그 제조방법 - Google Patents

항복비가 우수한 고강도 열연강판 및 그 제조방법 Download PDF

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Publication number
WO2021125563A1
WO2021125563A1 PCT/KR2020/015769 KR2020015769W WO2021125563A1 WO 2021125563 A1 WO2021125563 A1 WO 2021125563A1 KR 2020015769 W KR2020015769 W KR 2020015769W WO 2021125563 A1 WO2021125563 A1 WO 2021125563A1
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steel sheet
rolled steel
hot
yield ratio
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PCT/KR2020/015769
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English (en)
French (fr)
Korean (ko)
Inventor
박경수
김득중
김학준
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주식회사 포스코
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Application filed by 주식회사 포스코 filed Critical 주식회사 포스코
Priority to CN202080092129.3A priority Critical patent/CN114929907A/zh
Priority to US17/784,728 priority patent/US20230012991A1/en
Priority to JP2022538353A priority patent/JP7437509B2/ja
Priority to EP20901952.0A priority patent/EP4060057A4/en
Publication of WO2021125563A1 publication Critical patent/WO2021125563A1/ko

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the present invention relates to a hot-rolled steel sheet used as a material for parts and structural supports for automobile collision members, and more particularly, a post-process omitted type having excellent yield ratio while having high strength characteristics without undergoing subsequent processes such as heat treatment and cold rolling. It relates to a high-strength hot-rolled steel sheet and a method for manufacturing the same.
  • Steel materials used as materials for automobile collision member parts and structural supports are required to have high strength properties to ensure safety, and high tensile strength as well as high yield strength are also required.
  • Various studies related to precipitation strengthening or transformation strengthening are in progress to increase the strength of steel.
  • Patent Document 1 proposes a technique for securing strength by precipitation strengthening according to the addition of alloying elements.
  • Patent Document 1 attempts to secure high strength properties by adding alloying elements such as Ti, Nb, V, and Mo, but these alloying elements are expensive elements and their manufacturing cost is excessively increased, which is not preferable in terms of economic feasibility.
  • Patent Documents 2 to 4 propose techniques for securing strength and ductility by using a structure above ferrite and martensite, or by retaining austenite and utilizing a composite structure of ferrite, bainite, and martensite.
  • ferrite or retained austenite has excellent ductility but poor strength, so there is a technical difficulty in not sufficiently securing high strength characteristics.
  • Patent Document 1 Korean Patent Publication No. 10-2005-0113247 (2005.12.01)
  • Patent Document 2 Japanese Patent Laid-Open No. 2005-298967 (October 27, 2005)
  • Patent Document 3 US Patent Publication No. 2005-0155673 (July 21, 2005)
  • Patent Document 4 European Patent Publication No. 1396549 (March 10, 2004)
  • An object of the present invention is to provide a post-process omission type high-strength hot-rolled steel sheet having an excellent yield ratio and a method for manufacturing the same.
  • High-strength hot-rolled steel sheet having an excellent yield ratio according to an embodiment of the present invention by weight, C: 0.12% or more and less than 0.3%, Si: 0.5% or less (excluding 0), Mn: 0.1 to 2.5%, B: 0.0005 to 0.005%, P: 0.02% or less, S: 0.01% or less, the remaining iron (Fe) and unavoidable impurities, the microstructure contains more than 95% by volume of martensite, and the yield ratio (yield strength / tensile strength) is more than 0.75.
  • Cr 0.5% or less and Ti: may further include one or more of 0.005 to 0.2%.
  • the microstructure may include at least one of ferrite, bainite, retained austenite and carbide in a total of 5% by volume or less.
  • the tensile strength may be 1,250 MPa or more.
  • the yield strength may be 1,000 MPa or more.
  • the thickness of the hot-rolled steel sheet may be 1.5 mm or less.
  • the method for manufacturing a high-strength hot-rolled steel sheet having an excellent yield ratio according to an embodiment of the present invention, by weight, C: 0.12% or more and less than 0.3%, Si: 0.5% or less (excluding 0), Mn: 0.1 to 2.5%, B : 0.0005 to 0.005%, P: 0.02% or less, S: 0.01% or less, reheating the slab containing the remaining iron (Fe) and unavoidable impurities; Hot continuous rolling of the reheated slab to a thickness of 1.5 mm or less; cooling at a cooling rate of 50 to 1,000° C./s by starting cooling within 5 seconds after the end of hot rolling; and winding the cooled hot-rolled steel sheet.
  • the cooling end temperature in the cooling step may be 150 to 350 °C.
  • the slab, Cr: 0.5% or less and Ti: may further include one or more of 0.005 to 0.2%.
  • High-strength hot-rolled steel sheet having an excellent yield ratio according to an embodiment of the present invention by weight, C: 0.12% or more and less than 0.3%, Si: 0.5% or less (excluding 0), Mn: 0.1 to 2.5%, B: 0.0005 to 0.005%, P: 0.02% or less, S: 0.01% or less, the remaining iron (Fe) and unavoidable impurities, the microstructure contains more than 95% by volume of martensite, and the yield ratio (yield strength / tensile strength) is more than 0.75.
  • the present invention relates to a high-strength hot-rolled steel sheet having an excellent yield ratio and a method for manufacturing the same, and preferred embodiments of the present invention will be described below.
  • Embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. These examples are provided to those of ordinary skill in the art to which the present invention pertains in order to further explain the present invention.
  • High-strength hot-rolled steel sheet having an excellent yield ratio according to an embodiment of the present invention by weight, C: 0.12% or more and less than 0.3%, Si: 0.5% or less (excluding 0), Mn: 0.1 to 2.5%, B: 0.0005 to 0.005%, P: 0.02% or less, S: 0.01% or less, the remaining iron (Fe) and unavoidable impurities are included.
  • the unit is % by weight.
  • the content of C is 0.12% or more and less than 0.3%.
  • the content of Si is more than 0 and 0.5% or less.
  • the present invention limits the upper limit of the Si content to 0.5%. However, since Si not only acts as a deoxidizer but is also an element contributing to the improvement of strength of steel, the present invention may exclude 0% from the lower limit of the Si content.
  • the content of Mn is 0.1 to 2.5%.
  • Mn is an element that effectively contributes to the improvement of strength and hardenability of steel.
  • Mn forms MnS by combining with S, which is inevitably introduced during the manufacturing process of steel, it is also an element capable of effectively preventing the occurrence of cracks due to S. Therefore, the present invention limits the lower limit of the Mn content to 0.1% to achieve this effect.
  • the present invention limits the upper limit of the Mn content to 2.5% because it is not preferable in terms of weldability and economical efficiency as well as concerns about a decrease in tensile strength due to retained austenite. Accordingly, the Mn content of the present invention may range from 0.1 to 2.5%.
  • the content of B is 0.0005 to 0.005%.
  • the present invention limits the lower limit of the B content to 0.0005% in order to achieve such an effect.
  • B when B is excessively added, B may react with Fe to cause grain boundary embrittlement, so the present invention limits the upper limit of the B content to 0.005%. Accordingly, the B content of the present invention may range from 0.0005 to 0.005%.
  • the content of P is 0.02% or less.
  • P is a major element that segregates at grain boundaries and causes a decrease in the toughness of steel. Therefore, it is desirable to control the P content as low as possible. Therefore, it is theoretically most advantageous to limit the content of P to 0%.
  • P is an impurity that is unavoidably introduced into the steel during the steelmaking process, and controlling its content to 0% may cause an excessive process load. Therefore, the present invention limits the upper limit of the P content to 0.02% in consideration of this point.
  • the content of S is 0.01% or less.
  • S is a major element that forms MnS, increases the amount of precipitates, and embrittles steel. Therefore, it is desirable to control the S content as low as possible. Therefore, it is theoretically most advantageous to limit the content of S to 0%.
  • S is also an impurity that is unavoidably introduced into steel during the steelmaking process, and controlling its content to 0% may cause excessive process load. Therefore, the present invention limits the upper limit of the S content to 0.01% in consideration of this point.
  • Cr 0.5% or less and Ti: may further include one or more of 0.005 to 0.2%.
  • the content of Cr is 0.5% or less.
  • the present invention may further include Cr to achieve this effect.
  • excessive addition of Cr which is an expensive element, is undesirable from an economic point of view, and since excessive addition of Cr may deteriorate weldability, the present invention may limit the upper limit of the Cr content to 0.5%.
  • the content of Ti is 0.005 to 0.2%.
  • Ti is an element known to combine with C and N to form carbides and nitrides.
  • B is necessarily added to steel to ensure hardenability, but when N and B contained in steel are combined, the effect of adding B desired by the present invention cannot be achieved.
  • N when Ti is added, N before combining with B combines with Ti to form a nitride, so that the effect of adding B can be more effectively improved. Therefore, in the present invention, 0.005% or more of Ti may be added to achieve this effect.
  • the present invention may limit the upper limit of the Ti content to 0.2%. Accordingly, the Ti content of the present invention may be in the range of 0.005 to 0.2%.
  • the remainder of the steel sheet for enamel excluding the above-mentioned alloying elements consists of Fe and other unavoidable impurities.
  • the addition of a composition other than the steel composition mentioned above is not entirely excluded.
  • the inventors of the present invention conducted research on conditions in which high strength and yield ratio can be secured even without post-processing.
  • post-processing such as heat treatment and cold rolling should be performed in order to secure high strength and yield ratio.
  • high strength and yield ratio can be achieved by controlling not only the type of microstructure of the steel but also the fraction of specific microstructure. could be obtained at the same time.
  • the microstructure may include martensite of 95% by volume or more, and may include at least one of ferrite, bainite, retained austenite, and carbide in a total of 5% by volume or less.
  • the fraction of martensite may be 95% by volume or more relative to the volume of the entire hot-rolled steel sheet. Since the present invention contains more than 95% of martensite, which is a hard tissue, high strength and yield ratio can be secured at the same time. The inclusion of tissues other than martensite is not entirely excluded. However, since ferrite, bainite, carbide and retained austenite are undesirable for securing strength, their total fraction may be limited to 5% by volume or less, and more preferably, the total fraction may be strictly limited to 3% by volume or less. can In addition, the hot-rolled steel sheet may further include cementite and precipitates as a residual structure in addition to the above-mentioned structure.
  • the yield ratio (yield strength / tensile strength) of the hot-rolled steel sheet is 0.75 or more, the tensile strength (TS) of 1,250 MPa or more and the yield strength (YS) of 1,000 MPa or more can be satisfied.
  • the thickness of the hot-rolled steel sheet of the present invention is not particularly limited, it can effectively contribute to securing economic efficiency and lightness of the final product through thinning by having excellent strength and workability. Therefore, the thickness of the hot-rolled steel sheet according to an embodiment of the present invention may be 1.5 mm or less, and a more preferable thickness may be 1.4 mm or less.
  • the method for manufacturing a high-strength hot-rolled steel sheet having an excellent yield ratio according to an embodiment of the present invention, by weight, C: 0.12% or more and less than 0.3%, Si: 0.5% or less (excluding 0), Mn: 0.1 to 2.5%, B : 0.0005 to 0.005%, P: 0.02% or less, S: 0.01% or less, Cr: 0.5% or less, and Ti: at least one of 0.005 to 0.2%, the remaining iron (Fe) and unavoidable impurities to reheat the slab step; hot rolling the reheated slab; cooling at a cooling rate of 50 to 1,000° C./s by starting cooling within 5 seconds after the end of hot rolling; and winding the cooled hot-rolled steel sheet.
  • the slab of the above-described steel composition is reheated and hot rolled.
  • the slab manufactured by the conventional slab manufacturing process may be reheated in a certain temperature range.
  • the lower limit of the reheating temperature may be limited to 1,050°C
  • the upper limit of the reheating temperature may be limited to 1,350°C in consideration of economy and surface quality.
  • the reheated slab may be finish-rolled to a thickness of 1.5 mm or less by hot continuous rolling. Since the present invention intends to manufacture a thin-walled hot-rolled steel sheet by hot rolling, continuous rolling is performed in which the preceding and succeeding members are continuously rolled without separating them. Continuous rolling in which continuous rolling is performed is more preferable in terms of securing the thickness of the hot-rolled steel sheet.
  • the finish rolling temperature may be in the range of 800 to 950 °C.
  • cooling can be started within 5 seconds after the end of hot continuous rolling.
  • the present invention is intended to strictly control the microstructure of the hot-rolled steel sheet, and cooling is preferably started within 5 seconds immediately after hot rolling. This is because, when the time from the hot rolling to the start of cooling exceeds 5 seconds, ferrite, pearlite, and bainite, which are not intended by the present invention, may be formed by air cooling in the atmosphere. A more preferable time from hot rolling to the start of cooling may be within 3 seconds.
  • the cooling of the hot-rolled steel sheet may be performed up to a cooling end temperature of 150 to 350°C at a cooling rate of 50 to 1,000°C/s.
  • the cooling rate is less than 50° C./s, the transformation into ferrite, pearlite or bainite occurs during cooling, so there is a problem that the microstructure desired by the present invention cannot be secured.
  • the present invention does not specifically limit the upper limit of the cooling rate to secure the desired microstructure, but may limit the upper limit of the cooling rate to 1,000 °C/s in consideration of facility limitations and economic feasibility.
  • the cooled hot-rolled steel sheet can be wound.
  • the hot-rolled steel sheet manufactured by the above manufacturing method can secure a tensile strength (TS) of 1,250 MPa or more and a yield strength (YS) of 1,000 MPa or more without performing post-processes such as heat treatment and cold rolling, and the yield ratio (yield strength/tensile strength) can be secured at a level of 0.75 or higher, so post-processing can be omitted.
  • TS tensile strength
  • a hot-rolled steel sheet specimen was prepared using the conditions shown in Table 2 below.
  • Each slab was manufactured by a conventional manufacturing method, and was homogenized by reheating in a temperature range of 1,050 to 1,350 °C. Hot rolling was performed by continuous rolling.
  • Example 1 A 860 1.4 1.2 100 236 Example 2 A 874 1.4 1.5 200 208 Example 3 A 893 1.4 0.9 300 204 Example 4 A 919 1.4 0.8 100 289 Example 5 A 885 1.2 2.8 100 180 Example 6 B 916 1.4 1.2 100 246 Example 7 C 860 1.4 1.1 100 181 Example 8 D 861 1.4 0.5 100 227 Example 9 E 880 1.4 0.8 100 155 Example 10 F 897 1.4 1.1 100 245 Example 11 G 897 1.4 1.7 100 233 Comparative Example 1 A 885 1.2 2.6 100 140 Comparative Example 2 A 884 1.4 6.1 100 194 Comparative Example 3 A 884 1.4 5.7 100 129 Comparative Example 4 A 873 1.4 1.0 30 202 Comparative Example 5 C 860 1.4 1.1 100 451 Comparative Example 6 G 897 1.4 1.4 1.0 30 202 Comparative Example 5 C 860 1.4 1.1 100 451 Comparative Example 6 G 897 1.4 1.4 1.0 30 202 Comparative Example 5 C 860 1.4
  • microstructure and mechanical properties were measured and shown in Table 3 below.
  • the microstructure was measured using an optical microscope and a scanning electron microscope, and then evaluated through image analysis.
  • the pulling strength was evaluated by performing a tensile test in the C direction using the DIN standard.
  • Example 1 A 98 1,610 1,338 0.831
  • Example 2 A 97 1,619 1,261 0.779
  • Example 3 A 98 1,520 1,248 0.821
  • Example 4 A 96 1,621 1,325 0.817
  • Example 5 A 97 1,612 1,241 0.770
  • Example 6 B 96 1,287 1,086 0.844
  • Example 7 C 96 1,383 1,055 0.763
  • Example 8 D 96 1,674 1,351 0.807
  • Example 9 E 97 1,622 1,227 0.756
  • Example 10 F 98 1,648 1,365 0.828
  • Example 11 G 96 1,545 1,249 0.808 Comparative Example 1 A 97 1,624 1,187 0.731 Comparative Example 2 A 62 1,207 937 0.776 Comparative Example 3 A 62 1,211 878 0.725 Comparative Example 4 A 71 1,184 951 0.803 Comparative Example 5 C 61 973 845 0.868 Comparative Example 6 G
  • the fraction of martensite is less than 95% by volume, or the yield ratio (yield strength / tensile strength) is less than 0.75. indicated.
  • the cooling end temperature was as low as less than 150° C., and it could be confirmed that the yield ratio was poor.
  • Comparative Example 4 was a case where the cooling rate was low, and Comparative Example 5 was a case where the cooling termination temperature was high. The transformation into martensite did not sufficiently occur, and the tensile strength and yield strength desired by the present invention were not secured.
  • Comparative Example 6 was a case where the cooling termination temperature was low, and it was confirmed that the yield ratio was inferior.
  • Comparative Example 7 was a case where the content of C was low, and Comparative Example 8 was a case where the content of B was low, and the martensite fraction was less than 50% by volume, confirming that the tensile strength and yield strength were inferior.
  • Comparative Example 10 Ti was added but the content was low, and it was confirmed that the transformation to martensite did not sufficiently occur, and thus the tensile strength and yield ratio were inferior.
  • the hot-rolled steel sheet according to the present invention can secure the yield ratio and strength without undergoing subsequent processes such as heat treatment and cold rolling, and thus can be applied to materials such as parts for automobile collision members and structural supports.

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PCT/KR2020/015769 2019-12-20 2020-11-11 항복비가 우수한 고강도 열연강판 및 그 제조방법 WO2021125563A1 (ko)

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US17/784,728 US20230012991A1 (en) 2019-12-20 2020-11-11 High-strength hot-rolled steel sheet having excellent yield ratio, and method for manufacturing same
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EP20901952.0A EP4060057A4 (en) 2019-12-20 2020-11-11 HOT-ROLLED HIGH-STRENGTH STEEL SHEET HAVING EXCELLENT ELASTICITY RATIO AND ASSOCIATED MANUFACTURING METHOD

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